This invention relates to a method for production of a semiconductor device, more particularly to a group of improvements applicable to a method for production of a semiconductor device which is produced on a single crystalline semiconductor layer which is converted employing an energy ray irradiation process applied to a polycrystalline or amorphous semiconductor layer which is grown on a insulating layer which is produced on a silicon or quartz substrate.
A semiconductor device produced on an insulator has various advantages in comparison with a semiconductor device produced on a monolithic semiconductor substrate, because the parasitic effects are reduced or even eliminated, resulting in a higher integration and higher switching speed of the device. It is widely known that silicon on sapphire and silicon on magnesia spinel are respectively practical and available for potential use.
This category of semiconductor devices has gained more significance, particularly from a practical viewpoint, since the development of a process for converting of polycrystalline silicon or amorphous silicon into single crystalline silicon by irradiating the silicon with a laser or some other energy ray. Practically it is possible to produce a semiconductor device on a single crystalline silicon layer, which has been converted from a polycrystalline silicon layer grown on a silicon dioxide layer formed on a silicon substrate.
Due to the nature of the technical requirements of the energy ray irradiation process for conting of non-single crystalline semiconductor into single crystalline semiconductor, some possibilities remain for further improvement of the various processes. These improvements are based on and utilize the aforementioned crystal structure conversion process, particularly the process of converting polycrystalline silicon into single crystalline silicon by irradiation with a laser or some other energy ray.
Some of the possibilities for further improvement are itemized below:
1. Removing of the difficulty involved with the scribing process for splitting each chip of a finished semiconductor devices due to the increased hardness of the insulating layer. Particularly when scribing a semiconductor substrate or wafer with a diamond cutter, the blade of the cutter is easily damaged. Also, when scribing a semiconductor substrate employing laser cutting process, a longer time or higher power is required, causing drawbacks from the practical viewpoint.
2. Removing the difficulty of making a surface of the converted single crystalline semiconductor layer plain and smooth. Because perforations are required for an insulating layer necessary for the purpose of providing crystal nuclei, it is not necessarily easy to produce a plain and smooth surface on a single crystalline semiconductor layer which is converted from a non-single crystalline semiconductor layer, particularly at the perforations. Further, since a fine patterns are produced on the single crystalline semiconductor layer during the semiconductor device production process, the surface of the single crystalline semiconductor layer must be absolutely plain and smooth.
3. Removing the difficulty in producing of a planar type semiconductor device. It is not necessarily easy to produce a field insulator region for a single crystalline semiconductor layer converted from a non-single crystalline semiconductor layer by an energy ray irradiation process. Therefore, mesa type semiconductor devices have been predominantly produced employing such converted single crystalline semiconductor layers. Since a planar type semiconductor device is preferable rather than a mesa type semiconductor device, this difficulty in producing a planar type semiconductor device is a significant drawback.
4. Removing the possibility of damaging the converted single crystalline semiconductor layer during the high temperature oxidation process used to produce a field oxide layer. Experimental results show that the single crystalline silicon converted from the polycrystalline silicon by an energy ray irradiation process, is easily damaged when exposed to high temperature. Therefore, a method for producing a field oxide layer without damaging the converted single crystalline semiconductor layer is essential for efficient utilization of the process of converting polycrystalline semiconductor to single crystalline semiconductor layer by energy ray irradiation.
5. Developing a process for converting non-single crystalline semiconductor into single crystalline semiconductor without requiring crystal nuclei. A crystal nucleus is usually required as a seed to crystallize molten material. Therefore, a process not requiring crystal nuclei is highly desirable.
6. Developing a process which enables deep and uniform distribution of impurities, without lateral diffusion, in a semiconductor layer. With a heating system employing a furnace, it is difficult to realize deep and uniform distribution of impurities without lateral diffusion, because a wafer is exposed to a high temperature for a relatively long time. This results in an isotropic diffusion with non-uniform Gaussian distribution of impurities. which results in lower integration density semiconductor devices. A high surface impurity density caused by a non-uniform distribution of impurities in depth results in poor crystal quality, and low mobility of carriers. These drawbacks nullifies the various advantages of the process for converting polycrystalline semiconductor into single crystalline semiconductor by energy ray irradiation.
7. Developing a process for producing an embedded semiconductor resistor having a definite and uniform resistance and geometrical accuracy. The essential requirements of an embedded semiconductor resistor are low dispersion of resistance and low lateral diffusion. The former is the basic requirement of a resistor. The latter is necessary to increase the integration density of the device. The deep and uniform diffusion of impurities without lateral diffusion effectively realizes these requirements. However, it is difficult in a diffusion process employing a furnace to achieve the aforementioned deep and uniform diffusion of impurities without lateral diffusion. Therefore, developing a process to form deep and uniform diffusion of impurities without the lateral diffusion referred to in Item 6, can be applied to a process for producing an embedded semiconductor resistor having the desired characteristics noted above.
8. Improving a process for producing a mesa type semiconductor device utilizing a single crystalline semiconductor layer converted from a polycrystalline semiconductor layer by the aforementioned energy ray irradiation process. Albeit it is relatively easy to produce a mesa type semiconductor device rather than a planer type semiconductor device, the surface of the mesa side is rough and the edge of the mesa is sharp. These characteristics the metal wirings produced thereon to break.